The drainage of rain water and condensation from window sills is a long recognized problem in the window industry. The problem is particularly acute, but not confined to, windows sills for accommodating windows of the horizontally and vertically sliding type. In general, all window sills require some form of drainage system and the more complex a sill design, the more difficult it becomes to provide effective drainage at a reasonable cost. There are many prior art patents directed toward a drainage system for window sills which permits an efficient drainage of rain water and/or condensation while inhibiting the infiltration of wind-driven moisture into the interior of a building. Prior art patents known to be directed to this subject matter include:
Canadian Patent 996,820 - Paull PA2 U.S. Pat. No. 4,003,171 - Mitchell PA2 U.S. Pat. No. 4,156,998 - Grover et al. PA2 British Patent 1,537,347 - Clive Investments Pcy PA2 British Patent Application 2,022,179 - Braithwaite PA2 French Patent 2,288,211 - Monteau PA2 French Patent 2,240,341 - Schinhofen PA2 French Patent 2,250,888 - Monteau PA2 French Patent 2,336,860 - Schurmann
The above listed prior art patents describe a variety of drainage systems for windows and window sills, many of which are suitable for use with extruded type window frame sills. A common problem with these prior art systems is that they are complicated and therefore unreliable or they are difficult to manufacture and therefore not cost effective.
Building standards in many countries of the world have become extremely stringent in prohibiting the intrusion of wind blown rain water or condensation into the interior of a building through window structures. Window drainage systems are generally the most common source for the infiltration of wind-blown water through a window structure. Ideally, a window drainage system permits the ready evacuation of rain water and/or condensation while preventing heavy winds from forcing rain or condensation across the window sill and into the interior of a building.
Designing an effective drainage system is further complicated by modern extrusion profiles, especially plastic extrusion profiles which depend on design to minimize the use of plastic materials while maximizing the strength of an extruded window frame sill In order to maximize strength, the window frame sill of a modern window in extruded thermoplastic is a multi-chambered extrusion which complicates the problem of providing proper drainage.